A cellular telephone is one example of what is generally characterized as a “mobile station” (MS), a “mobile terminal” (MT), or even more generally as “user equipment” (UE). The term mobile terminal is employed hereafter for purposes of description. Telecommunications services are provided between a cellular telecommunications network and a mobile terminal over an air interface, e.g., over radio frequencies. An active mobile terminal communicates over the air interface with one or more base stations. The base stations are managed by base station controllers (BSCs), which in some systems, are known as radio network controllers (RNCs). The term RNC is employed hereafter for purposes of description. Radio network controllers are coupled to one or more telecommunications networks by way of one or more control nodes such as a mobile switching center (MSC) node for connecting to connection-oriented, circuit-switched networks such as PSTN and/or ISDN, and a general packet radio service (e.g., GPRS) node for connecting to connectionless, packet-switched networks such as the Internet.
A basic cellular communications system 10 is shown in simplified function block format in FIG. 1. An example core network 12 is connected to several radio network controllers 14 including RNC1, RNC2, and RNC3. Each RNC 14 controls the allocation of radio resources and radio connectivity operations for a set of cells: RNC1 controls cells 1:1-1:5, RNC2 controls cells 2:1-2:5, and RNC3 controls cells 3:1-3:5. The RNCs communicate by way of a signaling network, e.g., signaling system number 7 (SS7), and a transport network generally indicated at 16. Each cell is a geographical area where radio coverage is provided by radio base station equipment at the base station site. A base station may serve one or more cells. A handover occurs as a mobile terminal travels from an old cell to a new cell. This permits mobile terminals to “roam” considerable distances. Each cell is identified using a unique identity broadcast in that cell over a common broadcast channel.
As indicated in FIG. 1, the RNCs 14, the interconnecting signaling and transport network 16, and the radio base station equipment in each of the cells together comprise a radio access network (RAN) 20. Mobile terminals (MTs) 18 permit a subscriber access to telecommunications services offered by the core network 12 via the RAN 20. The radio access network 20 is responsible for the radio transmission and control of radio connections between the core network 12 and the mobile terminals 18.
In the present invention, different roles are assigned to RNCs in the RAN depending on circumstances, configurations, etc. One RNC role is that of a “controlling” RNC (CRNC) which controls the radio resources in its set of cells. In the example shown in FIG. 1, the RNC1 is the controlling RNC for cells 1:1 to 1:5, the RNC2 is the controlling RNC for cells 2:1 to 2:5, and the RNC3 is the controlling RNC for cells 3:1 to 3:5.
FIG. 2 shows adjacent cells in a cellular communications network. An active cell denotes the cell currently supporting a radio connection with a mobile terminal. Adjacent neighboring cells may be selected by the mobile terminal via forward handover to support the connection. Forward handover is a process where a mobile terminal itself continues an established connection between a core network and the mobile terminal as the mobile terminal moves between different cells in the radio access network. Contrasted with traditional handover, the mobile terminal in forward handover independently re-establishes the radio connection with a new cell. This re-establishment of the connection is performed without prior notification via the old cell. Nor is there advance preparation in the network to continue the communication via the new cell. It is the mobile terminal that initiates and orchestrates forward handover rather than the core network, the core network node (e.g., MSC), or the radio access network (RAN).
When the mobile terminal moves between cells controlled by different RNCs and performs forward handover, other roles are assigned to one or more of the RNCs for purposes of a connection between the core network and the mobile terminal. The RNC that controls the cell where the connection to the mobile terminal is initially established is assigned a “serving” RNC role for the duration of the connection. As the mobile terminal moves to new cells, the mobile terminal may reestablish the connection via a new cell controlled by another RNC which is then labeled as a “drift” RNC. For the connection to MT1, the controlling RNC of cell 1:2 (i.e., RNC1) acts as the serving RNC. For the connection to MT3, the controlling RNC of cell 2:5 (i.e., RNC2) acts as the drift RNC. The serving RNC role may be re-allocated to another RNC during the connection. The present invention may also be applied to such re-allocations.
A serving RNC (SRNC) has supervisory control of the mobile terminal connection within the radio access network 20 and provides a single interface to the core network 12 for that mobile terminal connection. The role of the drift RNC is to support the serving RNC with radio resources for the mobile terminal connection in cells controlled by the drift RNC. In the example shown in FIG. 2, RNC1 acts as the serving RNC for the connections between the core network and mobile terminals MT1, MT2, and MT3. After forward handovers, the connection to mobile terminal 3 (MT3) now includes a cell 2:5 that is controlled by RNC2. Thus, RNC2 functions as a drift RNC for this particular connection.
Referring again to FIG. 1, mobile terminal MT2 is in contact with the RAN 20 via cell 1:5 having neighbor cells 1:4 and 2:1. As a result of changed radio conditions detected from neighboring cell information, MT2 decides that the radio communication is to be reestablished via neighbor cell 2:1 controlled by RNC2 rather than RNC1. Accordingly, signaling and data transport between RNC1 and RNC2 are required to reestablish the radio connection. RNC1 acts as the serving RNC, and RNC2 acts as the drift RNC for MT2's connection. Furthermore, mobile terminal MT3 is in contact with the RAN 20 via cell 2:5 having neighbor cells 2:4 and cell 3:1. Because of changed radio conditions detected from neighboring cell information, MT3 decides that the radio communication is to be re-established via cell 3:1 controlled by RNC3. RNC1 acts as the serving RNC, and RNC3 acts as the drift RNC for the MT3 connection.
In both of these scenarios, signaling and data transport between serving RNC and drift RNC are required to reestablish the radio connection. Once a mobile terminal decides to perform the forward handover, it sends a cell update request message to the drift RNC, and the drift RNC sends a cell update message to the serving RNC. The serving RNC then returns a cell update accepted message to the drift RNC which passes that message back to the mobile terminal through the appropriate cell.
Since forward handover may involve more than one RNC, what is needed is an efficient way to route control messages and user data from the MT via the RAN 20 to the core network 12 and vice versa. This requires an efficient mechanism to route the control and user data between the RNCs in the RAN. Such efficient communications between RAN nodes or entities are advantageous in other scenarios.
One example scenario is found in the context of mobility management, i.e., messages related to paging and keeping track of the current location of the mobile terminal. In packet-switched communication services, radio resources are typically shared by plural mobile terminals and used only when either (1) the mobile terminal desires to transmit or (2) the network transmits to the mobile terminal. When a mobile terminal is connected with the network during a connection involving a packet-switched service, cell updating and registration area updating are employed for mobility management. After an active mobile terminal enters the coverage area of another cell, the mobile terminal re-establishes the radio connection with the new cell by means of a cell update procedure (“cell connected state”).
However, in idle periods of no data transfer, cell updating wastes radio resources, so registration area (RA) updating is used. In RA updating, the idle mobile terminal is in what is referred to hereafter as a “registration area connected state.” A registration area corresponds to a group of cells. Since traffic for a packet switched service is “bursty” in nature with long periods of no packet transfer, radio resources would be wasted if a radio channel was continuously assigned to a connection. Therefore, when the mobile terminal in an “RA connected state” moves into a new registration area, the mobile terminal updates the network with its current registration area using a registration area update procedure similar to the cell update procedure. Thereafter, the mobile terminal may move freely between cells belonging to the same RA without having to perform an update procedure. If a packet is to be sent from the network to the mobile terminal and the location of the mobile terminal is known only at the registration area level (rather than at a cell level), a paging message is broadcast in all cells belonging to the registration area where the mobile terminal made its last registration area update. When the mobile terminal answers the page from the particular cell where it is currently located, the mobile terminal enters the “cell connect state.” Both cell update related messages and registration area update related messages may often require message routing between RNCs in the RAN.
FIG. 3 illustrates an example where cells controlled by RNC1-RNC3 are grouped into registration areas, RA1-RA6, each consisting of one or several cells. Information transmitted on the broadcast channel in each cell may contain cell and registration area identifiers for purposes of registration control. As long as such cell and registration area identifiers broadcast by a specific cell contain the same cell and registration area identifiers assigned to the mobile terminal during the most recent cell or RA update procedure, the mobile terminal need not register. However, when the terminal mobile terminal does not recognize the broadcast cell and registration area identifiers in the cell, it initiates an RA update procedure.
An individual registration area (IRA) for a mobile terminal may be defined consisting of one or more registration areas (identified by RA identity) and/or one or several cells (identified by cell identity). Thus, a mobile terminal assigned the IRA of RA4, RA5, and cell 3:4 in FIG. 3, need not perform a new registration until entering cell 2:2 or 3:5. When there is information to be sent to a mobile terminal and the serving RNC must locate the mobile terminal on a cell level, the serving RNC initiates a paging procedure so that a paging message is sent in all cells belonging to the IRA. If the cells of the IRA belong to more than one RNC, the serving RNC sends paging request messages directly to each RNC that has a cell in the IRA. Alternatively, the serving RNC may send a paging request message to each RNC controlling the registration area(s) of the IRA, and to the RNCs controlling the additional cells of the IRA. The RNCs controlling the different registration area(s) will in turn request paging from other RNCs controlling cells within the registration areas. The mobile terminal response to the page may be received in a cell controlled by another RNC than the serving RNC, and possibly, by an RNC other than the RNC that acted as the drift RNC at the latest RA registration.
Accordingly, forward handover and mobile terminal location/mobility management operations require considerable signaling and data transport in the radio access network 20 between RAN entities like RNCs. The RAN also must keep track of which RNC controls the cell or registration area where the MT is currently known. It would therefore be desirable to have an efficient means to facilitate communication/information transfer between RNCs in the RAN that is transparent outside of the radio access network.
It is an object of the present invention to provide effective and efficient communication between mobile terminals and entities/nodes in the radio access network (e.g., RNCs).
It is an object of the present invention to provide and facilitate addressing of individual nodes in the RAN without each node having to know in advance the addresses of all other nodes.
It is another object of the present invention to provide and facilitate addressing nodes in the RAN without a location register common to the RAN where information related to a connection with a specific mobile terminal: is stored, e.g., an identity of current cell or registration area, a current serving RNC address, a current drift RNC address, a current temporary mobile terminal RAN identifier, etc.
It is an object of the present invention to provide and facilitate efficient radio connection re-establishment in a new cell belonging to another RNC than the RNC where the radio connection was originally established.
It is an object of the present invention to provide and facilitate efficient routing of control and user data after radio connection reestablishment in a new cell belonging to another RNC than the RNC where the radio connection was originally established.
It is an object of the present invention to provide and facilitate efficient routing of control and user data relating to paging and other mobility management messages.
In the context of a cellular communications system that includes a core network coupled to a radio access network (RAN) and a plurality of mobile terminals, a connection may be established between the core network and one of the plurality of mobile terminals through the radio access network. A temporary RAN identifier is associated with the mobile terminal for the established connection. The temporary RAN identifier is used to assist in the transfer of information pertaining to the established connection or to the establishment of that connection through the radio access network. The temporary RAN identifier is included in each data packet associated with the connection, and those connection data packets are routed through the RAN using the temporary RAN identifier incorporated in each connection packet.
The radio access network includes a first RAN node associated with a first geographical coverage area and a second RAN node associated with a second geographical coverage area. When the mobile terminal moves from the first coverage area to the second coverage area, the connection is re-established through the RAN by way of the first and second RAN nodes using the temporary RAN identifier. The temporary RAN identifier employed in packets corresponding to the established connection is used to direct those packets to and from the first and second RAN nodes. The first and second RAN nodes analyze packets corresponding to the established connection using a temporary RAN identifier included in each packet. From that analysis of the temporary RAN identifier, the first and second RAN nodes determine where packets are to be routed.
In a preferred example embodiment, the temporary RAN identifier may include (1) a RAN node identifier (the serving RNC identity) corresponding to the first radio network controller (RNC) through which the connection was initially established and (2) a local mobile terminal identifier unique within this RNC. The RAN node identifier and the local mobile terminal identifier are both employed when making initial contact in a new geographical coverage area. Thereafter, only a local mobile terminal identifier, unique within the current controlling RNC, is employed in order to save radio resources. Once the established connection is terminated, use of the temporary RAN identifier is discontinued.
Additional information may be provided along with the temporary RAN identifier in intra-RAN messages. Such additional information may include area information that permits the first RNC to route a message for the mobile terminal to the specific drift RNC controlling the area in which the mobile terminal is currently located. Such area information might include a registration area or a registration area and an additional cell outside of that registration area. The additional information may also include radio condition information.